1. Field of the Invention
This invention relates to a vacuum advancer which controls the ignition timing of an internal combustion engine of the spark ignition type, and more particularly, to improvement of a control device for a vacuum advancer.
2. Description of the Prior Art
There has been proposed a vacuum advancer adapted to be operated in response to the operational conditions of an internal combustion engine of the spark ignition type so as to delay the ignition timing within such an extent as allowed according to the operational conditions of the engine thereby reducing the emission of harmful compositions in the exhaust gases, such as nitric oxide, hydrocarbons, etc. As a control device for controlling such a vacuum advancer in response to the operational conditions of the engine, there is conventionally known a device such as shown in FIG. 1.
In FIG. 1, 1 designates a distributor, and 2 is a vacuum advancer mounted to the distributor to advance or delay the ignition timing determined by the distributor. The vacuum advancer 2 includes, as the operational elements thereof, a diaphragm 3, diaphragm chambers 4 and 5 disposed for opposite sides of the diaphragm and adjusting springs 6 and 7 for adjusting displacement of the diaphragm in response to the pressure difference acting on opposite sides of the diaphragm. Thus, the vacuum advancer is adapted to advance or delay the ignition timing according to the displacement of the diaphragm. The diaphragm chamber 4 is connected to a solenoid valve 9 by way of a conduit 8 and the diaphragm chamber 5 is connected to a solenoid valve 11 by way of a conduit 10. The solenoid valve 9 has first and second ports 13 and 14 the opening and closing of which are controlled by a core 12, wherein the port 13 is opened to the atmosphere, and the port 14 is connected by way of a conduit 15 to an inlet tube 16 of the carburetor (not shown). The conduit 15 opens to the inside of the tube 16 at a port 17. The solenoid valve 11 also has first and second ports 19 and 20 the opening and closing of which are controlled by a core 18, wherein the port 19 is connected by way of a conduit 21 to an inlet manifold 22, while the port 20 is opened to the atmosphere. The solenoid valves 9 and 11 are supplied with electric power from an electric power source 24 controlled by a computer 23 adapted to evaluate the operating conditions of the engine based upon the automobile speed, loading condition, temperature of the cooling water of the engine, etc. said computer determining whether or not the engine is in a condition to allow delaying of the ignition timing. In operation, when the solenoid valve 9, is not energized, the core 12 is in its lowered position as shown in the drawing to close the port 13 and to open the port 14, thereby introducing the vacuum in the inlet tube 16 of the carbureter into the diaphragm chamber 4. When the solenoid valve 9 is energized, the core 12 is raised to open the port 13 and to close the port 14, thereby to introducing atmospheric pressure into the diaphragm chamber 4. As for the solenoid valve 11, when it is not energized, the core 18 is in its lowered position as shown in the drawing to close the port 19 and to open the port 20, thereby introducing the atmospheric pressure into the diaphragm chamber 5. When the solenoid valve is energized, the core 18 is raised to open the port 19 and to close the port 20, thereby introducing the vacuum in the inlet manifold 22 into the diaphragm chamber 5.
In the abovementioned device, when the computer 23 determines that the ignition timing is not to be delayed, that is, under the conditions when the temperature of the cooling water of the engine is low, the automobile is running at a high speed, etc., the solenoid valves 9 and 11 are not energized, thereby maintaining the core 12 and 18 at lowered positions as shown in FIG. 1, whereby the diaphragm chamber 4 is exposed to the vacuum in the inlet tube 16 of the carbureter, while the diaphragm chamber 5 is exposed to the atmospheric pressure. In this condition, the diaphragm 3 is biased leftward as shown in FIG. 1 by a pressure difference applied at opposite sides thereof while compressing the adjusting spring 6, whereby a normal vacuum advancing action of advancing the ignition timing is performed. On the contrary, when computer 23 has determined that the ignition timing may be delayed as in a normal running condition, etc., the solenoid valves 9 and 11 are energized to move the cores 12 and 18 upward as seen in FIG. 1 thereby opening the ports 13 and 19 and closing the ports 14 and 20, respectively, whereby the atmospheric pressure is introduced into the diaphragm chamber 4, while the vacuum in the inlet manifold 22 is introduced into the diaphragm chamber 5. Thus, the diaphragm 3 is biased rightward as seen in FIG. 1 by a reversed pressure difference thereby compressing the adjusting spring 7 to delay the ignition timing.
Such a conventional control device of the vacuum advancer requires two solenoid valves, whereby it becomes expensive, requires a large space for mounting, and possesses the drawback that the chance of a malfunction is more frequent as the number of parts incorporated in the device are increased.